With feathers, birds can keep out of external cold, heat loss and as well as external heat
gained, for feathers can trap a layer of insulating air. The feathers are under muscular
control and can be held erect. When there is a breeze, the upright feathers direct the air
movement down to cool the skin.
Birds cannot sweat. They pant or flutter to
Some flesh-eating birds don' t need to drink as
they can get enough moisture from their preys. The seed-eating birds need to drink daily
and thus they are restricted in a number of places where they can nest.